Many international officials who were listed in papers revealing the offshore accounts of wealthy individuals, including associates of President Vladimir V. Putin of Russia, defended themselves on Monday.Published OnApril 4, 2016CreditCreditBrynjar Gunnasrson/Associated Press

WASHINGTON — A group of news media outlets published articles on Sunday based on what they said were 11.5 million leaked documents from a Panama law firm that helped some of the world’s wealthiest people — including politicians, athletes and business moguls — establish offshore bank accounts.

The German newspaper Süddeutsche Zeitung said its reporters had obtained the documents from a confidential source. The newspaper then shared the files with other media organizations, like The Guardian and the International Consortium of Investigative Journalists.

In an article, the investigative journalism organization said the documents revealed the offshore accounts of 140 politicians and public officials, including a dozen current and former world leaders and several individuals with close ties to President Vladimir V. Putin of Russia. The organization said reporters at 100 news media outlets working in 25 languages had used the documents to investigate the law firm, Mossack Fonseca, and its clients, including political figures in countries like Iceland, Pakistan and Saudi Arabia.

It is not illegal in many cases to have offshore bank accounts. But they are used in some instances by wealthy individuals and criminals to hide money and business transactions, and to avoid paying taxes.

The leak followed a series of high-profile breaches in recent years in which individuals working for governments or companies have amassed internal files and then given them to media organizations. In 2013, Edward J. Snowden, a contractor for the National Security Agency, gave reporters what intelligence officials have estimated was thousands of documents from the agency. Hundreds of articles have been published based on those documents.

The media organizations looking into Mossack Fonseca are expected to publish many more articles based on the new documents in the coming days.

The firm, which has dozens of offices around the world, has been investigated by law enforcement authorities in several countries over accusations of connections to money laundering.

In a lengthy statement provided to The Guardian, the firm said it could not respond to specific questions, but insisted that many of the individuals and companies named in the documents were never clients of Mossack Fonseca. The firm added that in many cases it was “legal and common for companies to establish commercial entities in different jurisdictions for a variety of legitimate reasons.”

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The documents revealed the offshore accounts of 140 politicians and public officials, including several individuals with close ties to President Vladimir V. Putin of Russia.CreditMaxim Shemetov/Agence France-Presse — Getty Images

“Our services are regulated on multiple levels, often by overlapping agencies, and we have a strong compliance record,” the firm said.

“In addition, we have always complied with international protocols” to assure “that the companies we incorporate are not being used for tax evasion, money laundering, terrorist finance or other illicit purposes,” it added.

According to the news reports, the documents related to Russia identified several officials with close ties to Mr. Putin, including two of his oldest friends, Sergei Roldugin, a cellist, and Yuri V. Kovalchuk, the principal shareholder of Bank Rossiya, a financial institution that has come under sanctions by the United States as the “cashier” of officials in the Kremlin.

The reports said Mr. Putin’s friends and associates had channeled $2 billion through a complex, deliberately convoluted network of offshore companies. Mr. Putin’s name appears on none of the records for the companies or the transactions, but Bank Rossiya and Mr. Roldugin do.

Mr. Roldugin acknowledged in an interview with The New York Times that he owned a share of Bank Rossiya, which he acquired in the 1990s, but offered few details about an investment that made him, on paper at least, a very rich man.

“I’ve got an apartment, a car and a dacha,” he said. “I don’t have millions.”

According to the disclosures, Mr. Roldugin holds similar shares of other companies, including an advertising firm founded by another close associate of Mr. Putin’s, Mikhail Y. Lesin, who was found dead in a hotel in Washington last fall.

Last week, the Kremlin’s spokesman, Dmitri S. Peskov, preemptively denounced the articles published on Sunday. He warned that the consortium had prepared an “information attack” against Mr. Putin and his associates, and described the articles as “an undisguised paid-for hack job.”

The revelations also touched Ukraine’s president, Petro O. Poroshenko, who was elected in the aftermath of the political upheaval in the country in 2014 that led to the annexation of Crimea and open conflict with Russia in eastern Ukraine.

Mr. Poroshenko, a tycoon with assets in television and a chocolatier before his entrance into politics, pledged to divest himself of his holdings but instead moved the assets into an offshore company in the British Virgin Islands, according to the consortium’s reporting. It said that Mr. Poroshenko, who has received political support from the United States, had not disclosed the arrangement.

The documents also contained information about how some foreign leaders used foundations and companies in Panama to anonymously own mining companies and real estate, according to the consortium.

Correction:

An article on Monday about roughly 11.5 million leaked documents from a Panama law firm that helped some of the world’s wealthiest people — including politicians, athletes and business moguls — establish offshore bank accounts misstated the year that Edward J. Snowden, a contractor for the National Security Agency, gave reporters documents from the N.S.A., and the number of documents he gave them. It was 2013, not 2014; and it was thousands of documents, not “at least 1.5 million.”